We have developed gain-coupled lasers based on metal gratings patterned laterally to the laser ridge. For narrow ridge waveguides, the evanescent field of the laser mode couples to the grating. The fabrication requires no overgrowth steps and can be applied to all material systems. Ridge-waveguide gain-coupled lasers with threshold current densities of 600 A/cm2 were obtained from InGaAs/AlGaAs GRINSCH structures. The continuous wave threshold currents are around 9 mA for a cavity with 600 μm length and 2.5 μm width. Monomode emission up to output power levels of 64 mW and sidemode suppression ratios of over 45 dB have been obtained.

We report the experimental demonstration of waveguides built around layer-by-layer photonic crystals. An air gap introduced between two photonic crystal walls was used as the waveguide. We observed full (100%) transmission of the electromagnetic (EM) waves through these planar waveguidestructures within the frequency range of the photonic band gap. The dispersion relations obtained from the experiment were in good agreement with the predictions of our waveguide model. We also observed 35% transmission for the EM waves traveling through a sharp bend in an L-shaped waveguide carved inside the photonic crystal.

We investigate quantum efficiency limitations in InGaAsP/InP multiquantum-well (MQW)laser diodes emitting at 1.5 μm. At room temperature, the internal differential efficiency above threshold is found to be reduced mainly by increasing Auger recombination and spontaneous emission within the quantum wells. These carrier loss increments are commonly assumed negligible due to MQWcarrier density clamping. Even with clamped average carrier density, increasing nonuniformity of the quantum well carrier population leads to enhanced losses. We analyze these loss enhancements using an advanced laser simulation software. Excellent agreement between measurements and simulations is obtained.

We report the formation of thin-filmwaveguides of organic crystals by precision optical polishing and the fabrication of an electro-optic intensity modulation device based on a thin-filmwaveguide of N,N-4′-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST®) as an overlay on a side-polished fiber (SPF). Successful fabrication of single-crystal DAST®waveguides with thicknesses in the 20–25 μm range have been produced. The waveguides were investigated via an evanescent coupling technique using side-polished fibers rather than traditional end-firing methods. Surface quality is believed to have been sufficient for low-loss propagation. Electrodes were added to the SPF/DAST® overlay architecture and intensity modulation observed out to 18 GHz. The device frequency response is believed to extend beyond 100 GHz under optimum conditions.

An ionically self-assembledmonolayer (ISAM) technique for thin-film deposition has been employed to fabricatematerials possessing the noncentrosymmetry that is requisite for a second-order, nonlinear optical response. As a result of the ionic attraction between successive layers, the ISAM filmsself-assemble into a noncentrosymmetric structure that has exhibited no measurable decay of at room temperature over a period of more than one year. The second-harmonic intensity of the films exhibits the expected quadratic dependence on film thickness up to at least 100 bilayers, corresponding to a film thickness of 120 nm. The polarization dependence of the second-harmonic generation yields a value of 35° for the average tilt angle of the nonlinear optical chromophores away from the surface normal.

This letter reports on the self-organizedgrowth of nanoscale dot-like CdSe-based islands during molecular beam epitaxy of CdSe/ZnSe nanostructures with a CdSe thickness between 0.75 and 3.0 monolayers. An increase in the nominal CdSe thickness results in a higher density of islands (up to and is accompanied by dramatic enhancement of the photoluminescence efficiency. The density of large relaxed islands appears to saturate at a value of Room temperature (Zn, Mg)(S, Se)-based optically pumped lasers with an extremely low threshold (less than 4 kW/cm2), as well as (Be, Mg, Zn)Se-based injection laser diodes using a single (2.5–2.8) monolayer thick CdSe active region, both demonstrating significantly enhanced degradation stability, have been fabricated and studied.

We have exposed 190 nm lines in photoresist by focusing a laser beam (λ=442 nm) in a solid immersion lens (SIL) that is mounted on a flexible cantilever and scanned by a modified commercial atomic force microscope. The scan rate was 1 cm/s, which is several orders of magnitude faster than typical reports of near-field lithography using tapered optical fibers. The enhanced speed is a result of the high optical efficiency (about of the SIL. Once exposed with the SIL, the photoresist was developed and the pattern was transferred to the silicon substrate by plasma etching.

The reflectivity of a microcavity filled with a quadratic nonlinear material is shown to be actively changed by the interaction of two waves. Within this microcavity, the reflection coefficient of a weak wave at the fundamental frequency is changed from almost 0% to a value in the vicinity of 100% by the simultaneous incidence of an intense wave at the second-harmonic frequency. This change in reflectivity is shown to be in a large degree insensitive to the input phase difference between the two waves.

An optically addressed ultraviolet lightmodulator has been demonstrated which exploits the optical anisotropy in a ZnO film epitaxially grown on (011̄2) sapphire. This device achieves both high contrast and high speed by exploiting the anisotropic bleaching of the anisotropic absorption and concomitant ultrafast polarization rotation near the lowest exciton resonances produced by femtosecond ultraviolet pulses. The resultant modulation is characterized by a contrast ratio of 70:1, corresponding to a dynamic polarization rotation of 12°, and it decays to a quasiequilibrium value within 100 ps.

A technique for the generation of dark pulse trains from continuous-wave (cw) light is presented. It consists of co-propagating a cw signal with intense pump pulses in an optical fiber where both the signal and the pump experience normal group-velocity dispersion. The pump imposes a positive frequency chirp on the signal through cross-phase modulation while normal dispersion tends to chip out the signal energy in the chirped region, thus leading to the generation of a dark pulse train with a repetition rate identical to that of the pump. A train of 30.3 ps dark pulses has been observed when using 31.7 ps pump pulses from an actively mode-locked fiber ring laser. The experimental results agree well with numerical simulations.

Time-resolvedphotoluminescence(PL)spectroscopy has been used to study the radiative recombination of excitons bound to ionized donors in GaN doped with both Mg and Si at concentrations of and respectively. Low temperature time-resolved, as well as integrated PL spectra, identify an ionized donor-bound (Si) exciton peak approximately 11.5 meV below and a neutral acceptor-bound exciton 20.5 meV below the free exciton peak. Rapid decay of the free exciton emission (⩽20 ps) implies that excitons are quickly captured by acceptors and ionized donors. We find the emission lifetime is consistent with previous measurements for GaN:Mg epilayers, while the lifetime of 160 ps is longer than that of the well studied neutral donor-bound exciton The measured lifetime, in comparison with and suggests that the state is stable at low temperature.

Radial distributions of axial stress across B/Ge- and Sn/Ge-codoped core fibers and a Corning standard single-mode fiber were measured before and after hydrogen loading under different conditions. A significant reduction of axial stress in the core of all investigated fibers is observed after hydrogen loading. The stress reduction in the core of hydrogen-loaded fibers is irreversible and depends strongly on the core dopants and the fiber drawing tension. The hydrogen-induced core stress reduction is believed to be related to the reactions between hydrogen and drawing-induced defects in the fiber core.

Azobenzene polymers and oligomers show intriguing surface relief features when irradiated with polarized laser light. We show through atomic force microscopic investigation of side-chain azobenzene polymers after irradiation through an amplitude mask that large peaks or trenches result depending on the architecture of the polymer. Extensive mass transport over long distances has been observed, paving the way for easy replication of nanostructures. We also show that it is possible to store microscopic images as topographic features in the polymers just through polarized light irradiation.

A Cu (400 Å)/Al (50 Å)/polyimide system showed larger adhesion strength than that of Cu (400 Å)/polyimide after ion beam mixing. X-rayemission spectroscopy was performed to elucidate the mechanism of adhesion enhancement of the ion beam mixed Cu (400 Å)/polyimide with a thin Al buffer layer.Cux-ray emission spectra showed the formation of a layer which is strongly correlated with the large adhesion strength of a Cu/Al/polyimide. A decrease in adhesion strength at an ion dose higher than was also explained by the formation of an amorphous carbon. This was understood by investigating C x-ray emission spectra. The overall spectroscopic results were in accordance with the behavior of quantitative adhesion strength.

We show that it is feasible to produce one- and two-dimensional nano-structure arrays by passing microsecond pulsed atomic beams through microsecond laser standing-wave patterns under completely off-resonant condition. This method enables fabrication of vertically heterogeneous nanostructures such as multilayers with one pulsed laser system.

We have investigated the effect of native oxide on the epitaxial SiGe from deposited amorphousGe on Si. Instead of epitaxialgrowth by molecular beam epitaxy or ultrahigh-vacuum chemical vapor deposition, the SiGe layer is formed by this simple process followed by an annealing step. As observed by transmission electron microscopy, the suppression of native oxide plays an important role to achieve epitaxial SiGe. The SiGe quality degrades with increasing native oxide thickness and becomes polycrystalline with a interfacial native oxide. On the other hand, single crystalline SiGe can be routinely formed from a HF-vapor treated Si surface.

We have studied compositional ordering in the near surface region of 3500 Å thick unstrained samples grown by chemical vapor deposition.Measuring asymptotic Bragg scattering along integer and half-integer truncation rods, we found a type of metastable ordering at this surface which is characterized by integer/half-integer reflections along the integer order truncation rods. We show unambiguously that those scattering features originate from a thin layer at the surface.Annealing at 750 °C extinguished these reflections irreversibly, while the reflections of the RS3 bulk structure were not affected. Anomalous scattering at the GeK edge also confirmed the existence of a new structure in the near surface region.

In this work, we present the experimental evidence of a polarity sensitive electro-optic response in a nematic liquid crystal. The liquid crystal cell was made by using a standard sandwich configuration, with one of the indiumtin oxide electrodes covered by a thin layer of tungsten trioxide deposited by sputtering. The optical response was inhibited when the electrode covered by film was anodically charged, while the usual optical response occurred under a reverse field. An ionic diffusion process was associated with the establishment of an internal electric field, which inhibited unipolarly the optical switching.

We analyze the photoluminescence(PL) in nanoporous Si (po-Si) doped with Er by electrochemicaldeposition and by spin-on doping. Two kinds of optically active Er centers appear in electrochemically doped po-Si with the main sharp and intense lines at 1.548 and 1.539 μm, respectively. The features characteristic for the spin-on doping method are: intense dislocation-related PL at 1.53 μm and strong luminescent activity of the silicagel used for Er doping. High-temperature PL observed up to 360 K is attributed to Er centers incorporated in the silica-like matrix at the oxidized surface of electrochemically doped po-Si and in erbium-containing silicagel.

The structural, electronic, and optical properties of single crystalline n-type 4H–SiC implanted with Ge atoms have been investigated through x-ray diffraction(XRD),Rutherford backscatteringspectroscopy(RBS),Raman spectroscopy, and sheet resistivity measurements. Ge atoms are implanted under the conditions of a 300 keV ion beam energy with a dose of X-ray diffraction of the Ge-implanted sample showed broadening of the Bragg peaks. A shoulder on the (0004) reflection indicated an increase in the lattice constant corresponding to substitutional Ge and implantation induced lattice damage, which was repaired through thermal annealing at 1000 °C. The diffraction pattern after annealing indicated improved crystal structure and a peak shift to a lower reflection angle of 35.2°. The composition of Ge detected through XRD was reasonably consistent with RBS measurements that indicated 1.2% Ge in a 1600-Å-thick layer near the SiC surface. Raman spectroscopy also showed fundamental differences in the spectra obtained for the Ge-implanted SiC (SiC:Ge) compared to a pure sample of SiC. Sheet resistivity measurements indicate a higher conductivity in the Ge implant by a factor of 1.94 compared to unimplanted SiC. These results have demonstrated the possibility of substitutional implantation of Ge atoms into the crystalline lattice of 4H–SiC substrates. The change in composition and properties may have numerous electronic device applications including high power, high temperature, optoelectronic, as well as high frequency device structures.